1. Field of the Invention
This invention generally relates to an improvement to a spline connection which is mainly used for a transmission gear assembled in a transmission, or the like. The spline connection uses the gear shaft of the transmission gear as a spline shaft, and a gear thereof as a spline boss, or a collar interposed between the gear shaft and the gear as a spline collar.
2. Description of the Relevant Art
A spline connection of the type shown in FIGS. 1 and 6 of Japanese Unexamined Utility Model Registration Application Publication No. 58736/1986, for example, is well known. Here, the spline connection is arranged such that the spline shaft thereof which is a gear shaft having a header passage for lubricant formed along the axial core line thereof is provided with oil passage so formed as to extend radially from the header passage and have each of their opening ends disposed in a valley between two neighboring outward spline teeth.
On the other hand, the spline collar thereof is provided with an oil port communicating the inside of the collar with the outside so that the lubricant may be supplied between the collar and the toothed wheel engaging with the outer periphery thereof.
In the spline shaft of the prior art described above, since the oil passages are formed at a diametrally reduced portion of the spline shaft so as to have the open end of each thereof disposed in the valley between the two neighboring outward spline teeth, torsional strength of the spline shaft is reduced. Consequently, the aperture of the oil passage is sacrificed for the necessary torsional strength and the header passage in the spline shaft is diametrally reduced in favor of a larger thickness of the spline shaft.
It might seem to make sense to arrange the oil passages such that the opening end may be located in the top surface of each of the outward teeth of the spline so as to have the oil passages formed in the diametrally larger portions of the spline shaft. In this arrangement, however, the strength of the top portion of the outward spline tooth becomes weak, especially when the width of the top surface of the outward spline tooth is approximately similar in measurement as the aperture of the oil passage. In addition, depending on machining precision of the oil passage, an off-centering of the passage can occur; thereby, causing the edge of the open end formation of a knife edge or burns which is detrimental to the durability of the spline.
As for the spline collar, the oil port of the spline collar must be communicated with the oil passage in order to be able to supply the lubricant to external gears, shift forks, or the like through the collar. Thus, when the spline collar is being fitted to the spline shaft, it is necessary to align, in phase, the spline collar with the spline shaft, but this is an extremely complicated work.
One way to solve the above-discussed problem may be to provide every inward spline tooth of the spline collar with a groove so formed as to cross the tooth transversely and extend alike in the same circumferential direction of the spline collar. The grooves would altogether then form an annular oil passage on the inner peripheral surface of the spline collar. Therefore, even when the spline collar is fitted to the spline shaft unaligned in phase with the latter, a sufficient quantity of lubricant can be supplied to the oil port through this oil passage. However, since it is usual to thinly form the spline collar itself with this arrangement, it is reasonable to assume that the spline collar strength is substantially lowered due to the formation of the grooves